Continuous process of electrodeposition

ABSTRACT

Process and apparatus for continuously electrodepositing metal of relatively uniform thickness on a moving metal substrate at extremely high plating rates.

United States Patent inventor Steve Eisner Schenectady, N.Y. Appl. No.134,295 Filed May 4, 1970 Patented Nov. 9, 1971 Assignee Norton CompanyTroy, NY. Continuation-impart of application Ser. No. 718,468, Apr. 3,1968, now abandoned.

CONTINUOUS PROCESS OF ELECTRODEPOSITION 8 Claims, 3 Drawing Figs.

US. Cl 204/35 R, 204/28, 204/36, 204/209, 204/D1G. 10 int. Cl C23] 5/50Field 01 Search 204/216,

References Cited UNITED STATES PATENTS 9/1910 Rosenberg 204/Dl9.

Rosenberg Bugbee E'delman Chessin et al..

Kiass et a1 Porzei Andersen Davidoff..... Whitaker.... 2/1962 Bailey eta1. 4/1967 Schwartz, Jr.

FOREIGN PATENTS 12/1924 Germany....

9/1967 France OTHER REFERENCES 204/D1G. 10 204/D1G. 1O 204/D1G. 1O204/D1G. 1O 204/D1G. 10 204/208 X 204/1 1 204/208 X 204/209 204/217 X204/36 1ndustria1& Eng. Chem., Vol. 61, No. 10, Oct. 1969, pp. 8- l7,204/D1G. 10

Primary E.raminer.1ohn H. Mack Assistant ExaminerR. J. Fay Anorneys-HughE. Smith and Herbert L. Gatewood ABSTRACT: Process and apparatus forcontinuously electrodepositing metal of relatively uniform thickness ona moving metal substrate at extremely high plating rates.

PATENTEDNUV 9 1971 a 7 i0 E6 3 INVENTOR STEVE E ISNER M/ffi ATI ORNEYCONTINUOUS PROCESS OF ELECTRODEPOSITION CROSS-REFERENCE TO RELATEDAPPLICATIONS This application is a continuation-in-part, of my copendingapplication Ser. No. 718,468 filed Apr. 3, 1968, for Electrodeposition(now abandoned), the entire disclosure of which is herein incorporatedby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the general field of electrodeposition. In particular, itrelates to continuously forming a metal coating by means ofelectrodeposition on a metal substrate.

2. Description of the Prior Art The electrodeposition of metal over thepast several decades has assumed a prominent position in science andindustry, so that today a sizable portion of the yearly output of metalsis consumed in such processing. A large variety of electrodepositionprocesses are known and currently in use. Electrodeposited metalcoatings, as is well known, are used in providing, among otherfunctions, hard wear-resistant surfaces on less wear-resistant metals,surfaces having desirable aesthetic properties on base metals not sopleasing in appearance, costing much less, or structurally desirable, orthe like, and surfaces more resistant than the base metal to variouscorrosive atmospheres.

In general, electrodeposition of a metal coating on another surface is aslow process. Many efforts have been made in the past to increase thespeed of these processes, but have met with only limited success.Quality is usually more important in electroplating than is rate ofdeposition, and, therefore, speed is almost invariably sacrificed when agood quality electrodeposit is sought. In continuous electrodepositionprocesses, where speed or rate of deposition is a particularly importantfactor, extremely long plating lines have been used to obtain anincreased rate of metal substrate movement while maintaining sufficientcontact with the electrolytic solution to obtain a commerciallydesirable electrodeposit of the required thickness on the substrate.

In commercial electroplating, the preparation of the substrate forelectrodeposition has been as important to a successful process as theelectrodeposition itself. This was particularly true when platedarticles having a high quality finish were desired. The particular typeof preparation of the substrates for electrodeposition depended on thesubstrate material, its condition, shape, size, composition, surfacecondition, and other factors. However, to provide good adhesion betweenthe electrodeposited metal and the substrate it was generally deemednecessary to clean the substrate surface of any foreign matter, e.g.protective oils, dust deposits, salts, etc. Removal of dirt, grease andlacquers was usually accomplished by using some form of alkalinecleaner, often containing oxide solvents such as cyanides and detergentssuch as sodium phosphate, as well as other materials. The alkalinecleaners were used alone or in combination with electrolytic cleaningwhere the object to be plated is alternately made anode and cathode. Atother times grease and dirt were removed by organic solvents, usually ofthe petroleum type. Inasmuch as the metal deposited follows the contoursof the substrate on which it is deposited, generally smooth finisheswere produced only on substrates having smooth surfaces. For thisreason, substrate surfaces, which were rough due to scratches, or otherdiscontinuities andimperfections were often treated by mechanicalcleaning methods, such as sandblasting or the object was pickled in somesuitable acid. Oftentimes, an electroplating line involving continuouselectrodeposition included a number of these pretreatment steps incombination with the electroplating. These combination treatmentsrequired rather elaborate apparatus. The pretreatment processes involvedelaborate schemes for handling the workpiece, thus requiring additionalpersonnel, equipment and space, all of which added considerably to theoverall manufacturing cost of the electrodeposited metal product.

In general, it has been found desirable, and in some instancesnecessary, to include in the electrolytic solution, in addition to thesalt containing the metallic ion or radical, a socalled addition agent.These agents were used for a number of purposes, including inhibition ofdendritic or columnar growth, creation of some preferred orientation ofthe metal crystals, and for their capability to interfere with or impedecrystal growth, thus resulting in deposits having small crystals. Theuse of addition agents in the electrolytic solutions produces someparticular advantage; however, their use can also introduce somedisadvantages into the plating process. Thus, an addition agent may befound suitable in enhancing one property, e.g. brightness in a deposit,while adversely effecting other properties, e.g. hardness. Oftentimes,extreme caution had to be exercised in controlling the size and amountof addition agent used in the electrolytic solution. Moreover, withcertain electrolytic solutions the rate of deposition was limited by theuse of addition agents.

SUMMARY OF THE INVENTION In general, my invention provides a process bywhich a metal substrate can be plated continuously with a metal coatinghaving a relatively uniform thickness and smoothness. The processprecludes dendritic growth in the deposit.

Quite advantageously, my process minimizes the amount of preparation ofthe substrate required for electroplating. The prior art necessity ofusing chemical cleaning materials, mechanical preparation techniques,and electrolyte addition agents therein to inhibit dendritic growth orto obtain microleveling during operation are essentially all eliminatedby my process.

In the performance of my invention the cathode surface and/or cathodicdeposit is mechanically activated" simultaneously with deposition ofmetal ions thereon. Although the mechanism of the mechanical activation"is not totally understood, it is theorized such consists of severalactions taking place essentially simultaneously. It appears to involveremoval of the polarization layer with simultaneous distortion of thecrystal lattice structure of the deposit. While activation" may involveremoval of a minute amount of metal from the surface being activated,such removal is not absolutely necessary. The activation" processrequires distortion of the metal deposit sufficiently to produce thereina scratch pattern which oftentimes is visible to the naked eye or undera magnification of 2,000 power or less, but in any event it is visibleunder a magnification of less than 10,000 X. This scratch pattern inmany instances involves mere plowing" or rearrangement of the surface,rather than actual removal of metal from the surface. In any event, andwhatever the mechanism involved, activation" is produced by contactingthe metal surface with an activating means, hereinafter more fullydescribed, which moves relative to the metal surface. The activation ofthe metal layer results in a markable increase in the rate ofelectrodeposition as is reflected in the ability of the present processto operate at current densities far in excess of prior art currentdensities of -150 amps per square foot.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understoodby reference to the drawings in which like numerals refer to the sameparts in the various Figures.

FIG. I is a schematic representation of apparatus which may be used inthe practice of my invention.

FIG. 2 is a schematic representation of a variation of the apparatus ofFIG. 1.

FIG. 3 is a cross-sectional view of the activating means of FIGS. 1 and2.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 of thedrawings, there is shown a tank 26 containing an electrolytic solution24. A metal strip 10 on which is to be provided an electrodepositedmetal coating is passed from a source thereof, such as a coil 13, aroundguide roll 14, across electrical contact 115 and pressure roller 25,over guide rolls 16, 17 and 18 to wind up means (not shown in thedrawing) wherein the metal strip 10 is wound into a coil 19. The metalstrip H is supplied with negative current by electrical contact 15 andthereby metal strip becomes the cathode in tank 26.

In contact with metal strip 10 as it passes over electrical contact 15,pressure roller 25 and roller 16 is activating means 20 which takes theform of a continuous belt which is mounted on rollers 21 and 22. One orboth of rollers 21 and 22 may be rotatively driven, thereby causingactivating means 20 to move in a linear path. The direction of travel ofactivating means 20 is preferably opposite to that of metal strip 10;however, it can move in the same direction provided that its linearvelocity is at least percent faster or slower than that of metal strip10.

Anode 23 is located near pressure roller 25 with metal strip 10 andactivating means interposed between anode 23 and roller 25. Roller ismovable laterally as is shown in FIG. 1. When roller 25 is moved towardsanode 23, the metal strip 10, activating means 20 and anode 23 arebrought into rubbing contact. The pressure contact between activatingmeans 20 and the strip 10 can thus be regulated by the movement ofpressure roller 25. With such arrangement the pressure contact betweenactivating means 20 and the sheet metal strip 10 can be regulated asdesired, depending upon the particular metal being deposited. With thedeposition of some metals the pressure will be desirably less than inthe deposition of other metals to avoid removing an undesirable amountof the metal just deposited. The spacing between the anode and pressureroller can be varied as desired, depending upon the activating meansused, its thickness, compressibility, relative speeds, the pressurecontact desired, etc. The maximum gap distance is fixed by the IR dropconsidered acceptable for the particular operation.

Metal strip 10 can be any metal on which a metal coating is desired.Merely by way of example it may be copper, tin, zinc, nickel, iron,brass, steel or alloys thereof. The metal strip 10 can be of any desiredwidth and thickness limited only by the size of the particular apparatusused in the practice of the invention. The electrolytic solution 24 canbe any solution desired, taking into consideration the particular metalcoating which is to be provided.

In the practice of my invention various metals can be used as thecathode. The anode may be of the consumable type, i.e., the same metalto be deposited, or of the inert type, eg an anode composed of lead or alead composition containing from about 6-15 percent antimony. In theevent a nonconsumable or inert anode is used, the concentration of theelectrolytic solution 24 must be adjusted periodically as is well knownin the electroplating art.

The activating means has supported at least on its surface, in closelyspaced relationship to one another, a plurality of small relativelyinflexible particles, as fully described in my copending application,Ser. No. 718,468, mentioned earlier. The activating means can be madefrom a variety of materials including open-weave fabrics or compressednonwoven substrates. A preferred activating means has been discovered tobe a compressed nonwoven abrasive member having a high degree ofresiliency and porosity. Such an activating means is more fullydescribed in my copending application, Ser. No. 718,468, mentionedearlier and in the examples hereinafter given.

A variation in the apparatus of FIG. 1 is shown in FIG. 2. In FIG. 2there is shown a housing 33 which encloses the activating belt systemcomposed of activating means 32 which again is in the form of acontinuous belt which is mounted on rollers 31 and 34. One or both ofrollers 31 and 34 may be rotatively driven, thereby causing activatingmeans 32 to move in a linear path.

A metal strip on which is to be provided an electrodeposited metalcoating is passed from a source thereof,

such as a coil 35, around electrical contact 36 to windup means (notshown in the drawing) wherein the metal strip 30 is wound into a coil37. The metal strip 30 is supplied with negative current by electricalcontact 36 and thereby acts as the cathode in the area ofelectrodeposition.

Anode 38 is located near electrical contact 36 with metal strip 30 andactivating means 32 interposed between anode 38 and electrical contact36. Electrical contact 36 is movable laterally as is shown in FIG. 2.When electrical contact 36 is moved towards anode 38, the metal strip30, activating means 32, and anode 38 are brought into rubbing contact.The pressure contact between activating means 32 and strip 30 can thusbe regulated by the movement of electrical contact 36 similarly to thesystem described for FIG. 1.

The anode 38 and the area of electrodeposition on strip 30 are notimmersed in the electrolyte as in FIG. I, but rather are flooded withelectrolyte by a pump 39, pipe line 40 and trough 4]. The electrolytesolution drains to the bottom of housing 33 forming a pool 42 whichsupplies the intake of pump 39 with electrolyte.

FIG. 3 shows a highly enlarged and idealized portion of one type ofactivating media suitable for use in the present invention. Referencenumeral represents fibers of a nonwoven web (nonconducting fibers aspolyethylene terephthalate or the like) which are anchored one to theother at their points of intersection by an adhesive binder 86. Aplurality of small, hard, discrete particles 87 are positioned on thefibers 85 and in the present illustration are held to such fibers by theadhesive 86. At least some of the fibers 85 extend relatively parallelto the cathode face 89 as shown at 88 to form thin-walled cells orelectrolyte sweeping members which provide fresh electrolyte constantlyto the activated plating surface. (For purposes of illustration, theactivating particles 87 are here shown at some distance from the cathodeface 89 and associated electrodeposit 90 although in operation of thepresent apparatus they would be in contact therewith.)

The following specific examples will illustrate more clearly thepreferred embodiments of my invention.

EXAMPLE 1 Using the apparatus as shown in FIG. 2 of the drawing steelshim stock (4 mils thick and 3 inches wide) as obtained from a steelsupplier was electroplated without any prior cleaning or surfacetreatment with a copper deposit from a solution of copper sulfatecontaining 45 grams of copper sulfate per liter. This solution was heldat a temperature of approximately 75 F. The activating means used inthis instance, was made from a nonwoven web of polyester fibers bondedwith an acrylonitrile-melamine resin adhesive and roll coated with aphenolic adhesive and abrasive grain as described in my copendingapplication, Ser. No. 718,468, mentioned earlier. The apparatus wasadapted to allow the shim stock cathode to roll past the activatingmeans over a 1 inch diameter steel electrical contact disposed laterallyopposite the anode, and laterally with respect to the activating means.The anode utilized was a lead slab 4 inches X 6 inches X one-fourthinch. The activating means, in the form of a continuous belt, operatedat a linear speed of 1,050 feet per minute.

The electrical contact was adjusted so as to put the shim stock cathodein engagement with the activating means and anode at an applied load ofabout 29 p.s.i. The contact area made by the shim stock on the cathodewas about one-fourth inch X 3 inches.

A cathode current density of 5,700 amps per square foot (a.s.f.) wasmaintained. The rate of travel of the shim stock over the electricalcontact was 12 feet per minute.

After rinsing with tap water the copper deposit was observed to have auniform bright appearance. The copper deposit was determined to be 0.1mil thick uniformly over the entire strip.

When the copper deposited steel shim stock was crinkled and bent double,the copper deposit did not crack or peel off,

thus showing outstanding adhesion between the copper deposit and thesteel substrate. This is indeed surprising because according to priorart teachings steel which has been plated with copper without a strikeusually has shown poor adhesion.

EXAMPLE 2 In a manner similar to that disclosed in example 1, tin wasplated on a brass substrate from a solution containing 36 oz./gal. ofS,,SO and 36 oz./gal. of H 80 The tin deposit on subsequent examinationshowed excellent adhesion to the brass substrate.

EXAMPLE 3 In a similar manner to that disclosed in example 1, copper wasplated on a mild steel substrate from a solution at room temperature ofcopper sulfate containing 45 grams of copper sulfate per liter. Thesteel shim stock was advanced at at rate of 3 feet per minute and theactivating belt speed was 1,350 feet per minute. The current density was725 amps per square foot and the pressure exerted on the activating beltby the cathode was 1.18 pounds per square inch.

A pressure sensitive adhesive tape adhesion test was performed in thefollowing manner. A cross was scribed into the electrodeposit with aknife, a piece of adhesive tape was placed on the electrodeposit at anangle of 45 to the scribed lines. The tape was then pulled from theelectrodeposit. The test was repeated at a direction 90 to the firsttape direction. For the deposit obtained in example 3, no copper waspulled off with the tape showing good adhesion of the copper coating tothe steel substrate.

Many different embodiments of the invention will readily occur to thoseskilled in the art of electroplating, and the specific embodiments ofthe invention are presented by way of illustration only and not aslimiting the invention. Therefore, the scope of this invention is to belimited only by the appended claims.

We claim:

1. A process for electrodepositing metal on a thin metal substrate whichcomprises:

a. Providing a supply of thin metal substrate in the form of longlengths of strip stock;

b. Continuously passing said strip stock into and through anelectroplating zone where metal is deposited on the surface of saidstrip stock;

c. Providing in said electroplating zone continuous activation of thesurface of said strip stock and of the entire surface of the metal beingdeposited thereon by contact with a plurality of small spaced activatingparticles secured to a supporting matrix; and

d. Continuously removing said strip stock and the metal depositedthereon from said electrodeposition zone.

2. A process, according to claim 1, wherein the continuous activation ofsaid surfaces results in surface scratches visible under a magnificationof less than 10,000 X.

3. A process, according to claim 2, wherein the sheet metal stock to becoated is steel and the electrodeposited metal is selected from thegroup consisting of zinc, copper, tin, nickel and alloys thereof.

4. Apparatus for the high speed electrodeposition of metal onto a thinmetal substrate which comprises:

a. Means to continuously feed a thin metal substrate from one station toa second station;

b. Means to electrically connect said thin metal substrate intermediatesaid stations to a source of negative potential;

c. Anode means positioned adjacent said thin metal substrateintermediate said stations and electrically connected to ground;

d. Movable nonconductive activating means comprising a plurality ofsmall, hard particles secured to a supporting matrix between and incontact with said anode and at least a portion of said thin metalsubstrate intermediate said stations; e. Means to move saidnonconductive activating means relative to and in contact with at leastsaid portion of said thin metal substrate; and

. Means to supply electrolyte to said portion of said thin metalsubstrate in contact with said activating means whereby the surface ofsaid thin metal substrate and of the metal deposited thereon in saidportion thereof is mechanically activated resulting in a rapid buildupof an electrodeposit on said thin metal substrate.

5. Apparatus as in claim 4 wherein said activating means comprises anelectrolyte-permeable matrix having a plurality of small nonconductiveparticles adhered thereto in fixed spaced relationship one to the other.

6. Apparatus as in claim 5 wherein said matrix comprises a porousnonwoven web.

7. Apparatus as in claim 5 wherein said matrix comprises a

2. A process, according to claim 1, wherein the continuous activation ofsaid surfaces results in surface scratches visible under a magnificationof less than 10,000 X.
 3. A process, according to claim 2, wherein thesheet metal stock to be coated is steel and the electrodeposited metalis selected from the group consisting of zinc, copper, tin, nickel andalloys thereof.
 4. Apparatus for the high speed electrodeposition ofmetal onto a thin metal substrate which comprises: a. Means tocontinuously feed a thin metal substrate from one station to a secondstation; b. Means to electrically connect said thin metal substrateintermediate said stations to a source of negative potential; c. Anodemeans positioned adjacent said thin metal substrate intermediate saidstations and electrically connected to ground; d. Movable nonconductiveactivating means comprising a plurality of small, hard particles securedto a supporting matrix between and in contact with said anode and atleast a portion of said thin metal substrate intermediate said stations;e. Means to move said nonconductive activating means relative to and incontact with at least said portion of said thin metal substrate; and f.Means to supply electrolyte to said portion of said thin metal substratein contact with said activating means whereby the surface of said thinmetal substrate and of the metal deposited thereon in said portionthereof is mechanically activated resulting in a rapid build-up of anelectrodeposit on said thin metal substrate.
 5. Apparatus as in claim 4wherein said activating means comprises an electrolyte-permeable matrixhaving a plurality of small nonconductive particles adhered thereto infixed spaced relationship one to the other.
 6. Apparatus as in claim 5wherein said matrix comprises a porous nonwoven web.
 7. Apparatus as inclaim 5 wherein said matrix comprises a porous open-weave fabric. 8.Apparatus as in claim 5 wherein said particles comprise abrasive grains.